Carry over cooking or resting is where food (usually meat, fish or eggs) retains heat and continues cooking even after being removed from the heat source. The larger and denser the object being heated the greater the effect of carry over cooking. After being removed from the heat source (oven, barbecue grill, etc.) the internal temperature can continue to increase. This means that when cooking large meat cuts, the meat should be rested before serving to allow heat to distribute from the warmer outside to the cooler middle, also allowing juices to distribute throughout the meat.
A steak that is not rested will 'bleed' profusely if cut immediately after cooking, yet one that is rested will not.